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Homework Help: The Force of Gravity Question

  1. Jul 21, 2011 #1
    On Earth, the gravitational field intensity is 9.8 N/kg. Mercury has a mass of 3.28 x 1023 kg and a radius of 2.57 x 106 m. Calculate the gravitational field intensity on Mercury in N/kg.


    g = 9.8 N/kg (on earth)
    m = 3.28 x 10^23 Kg
    d = 2.57 x 10^6m


    g = ?



    I was just wondering what given would be used and what equation would you use to solve this question; F = Gm1m2 / d^2 or F = mg.
  2. jcsd
  3. Jul 21, 2011 #2
    What is the definition of little g? What is the definition of big G? (I don't mean the value. I mean the definition from a conceptual sense.)

    One of those two is universally applicable. The other is not. That should give you a clue as to which equation to use.
  4. Jul 21, 2011 #3
    G in the universal gravitational constant (6.67 x 10^-11 Nm^2/kg^2). So, I have to F = Gm1m2 / d^2 to solve this question...but isn't m2 (mass of Earth) not given?
  5. Jul 21, 2011 #4
    Why do you care about the mass of the Earth? Where are you performing this calculation?

    Consider the units involved. The problem asks for the gravitational field intensity, which has units of N/kg. Is this the same thing as gravitational force? What are the units of gravitational force? What do you need to do to make the units match?
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